1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a multilayer metal interconnection.
2. Description of the Prior Art
With the enhancement of the level of integration of semiconductor devices the multilayer metal interconnection has become to be employed extensively. A multilayer metal interconnection is formed ordinarily by alternately laminating a metal wiring layer consisting of aluminum (A1) or tungsten (W) and an interlayer insulating film after coating the surface of a semiconductor substrate which was subjected to an impurity diffusion process or the like for the formation of semiconductor devices with an insulating film such as a silicon oxide film. The interlayer insulating film between two metal wiring layers consists of a lower layer silicon oxide film by a chemical vapor deposition (CVD) method, a coating (spin on glass (SOG)) film, and an upper layer silicon oxide film by the CVD method which covers the coating film (see Japanese Patent Application Laid Open No. 57-100748). Since the right-angled parts of the edges of the metal film pattern of the metal wiring layer are substantially dulled by the above-mentioned coating film, and the steep level difference due to the lower layer metal wiring is ameliorated, making the surface of the interlayer insulating film covering the wiring layer more flat. As a result, even in the upper metal wiring layer formed on the surface of the interlayer insulating film over the lower metal wiring layer, corresponding to the region of the lower metal wiring layer where a plurality of extra fine metal film stripes are arranged parallel with each other at the minimum allowable space according to design rules, there will not occur too much deterioration in the step coverage, that is, the ratio of the smallest thickness of the metal wiring at the step part to the thickness of the metal wiring at the flat part.
However, when the lower metal wiring layer includes a part where just two extra fine metal film stripes are formed parallel with each other away from other wiring pattern at the minimum space, the flatness of the interlayer insulating film is deteriorated because it is not possible to thoroughly fill in the space between the two metal film stripes in forming the interlayer insulating film that covers the lower metal wiring layer. Accordingly, if an upper layer metal wiring is formed on an interlayer insulating film with a low degree of flatness as in the above, the step coverage of the wiring film is reduced and the disconnection of the wiring is liable to take place. Even if it does not lead to the disconnection of the wiring, there will be generated, in the wiring film, portions with very small thickness which induce electromigration or stress-migration, deteriorating the reliability and the yield of the semiconductor device.